This invention relates to titanium dioxide coated micaceous iron oxide pigments having improved weatherability and lightfastness. It also relates to the production of such pigments.
Japanese Patent Publication No. 7176/1976 assigned to the assignee of this application discloses a pigment composed of flaky micaceous iron oxide (MIO) having a thin coating layer of a metal oxide such as titanium dioxide. This coating layer is transparent and has a high refractive index so that the pigment exhibits a unique metallic glamor owing to the interference of light. It has been found, however, that the above pigment tends to lose its unique glamor upon exposing to light for a long period of time particularly under outdoor conditions. This is because the TiO.sub.2 crystals forming the coating layer are of anatase type. Attempts have been made to produce a similar pigment coated with rutile type TiO.sub.2 which is known to have a greater weatherability than antatase type TiO.sub.2. Unfortunately, since the transition of TiO.sub.2 to rutile requires a higher temperature and/or a longer period of time than the transition to anatase, the above attempts failed to produce a pigment having the same or similar optical properties as the prior art pigment. This is because th MIO substrate is not stable and/or reacts with TiO.sub.2 under such conditions.